Monolithic integrated circuits (ICs) generally comprise a number of passive devices, such as resistors, and/or active devices, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), or the like, fabricated over a substrate. FIG. 1A is a plan view of a conventional monolithic compound resistor 110 disposed over a substrate isolation dielectric 106. FIG. 1B is a cross-sectional view of conventional compound resistor 110 that consists of two resistive materials, 115 and 120, stacked vertically. Resistor contacts 130 are made at two ends of compound resistor 110 and interconnected with other passive and active devices into an IC. Through selection of materials 115 and 120, and a ratio of their z-thicknesses, compound resistor 110 may have a wide range of resistivity and thermal properties.
However, the multiple resistive materials employed in conventional compound resistor introduce problems not found in homogenous thin film resistor designs. For example, the multiple resistive materials often have very different thermal properties and when the compound resistor experiences Joule heating during operation, thermal expansion mismatch can be an issue. Delamination of the resistor material(s) and/or mechanical stress-induced voiding/cracking within the materials may result in an uncontrolled change of resistance value and/or an open circuit condition. Another concern with a conventional compound resistor is the potential for reaction with surrounding interlayer dielectric (ILD). Chemical reactions and/or solid-state diffusion with the ILD material may occur along the entire resistive length of the multiple resistive materials exposed to the ILD.
Compound resistor structures that are less susceptible to these failure modes would therefore be advantageous in advanced IC structures.